It is estimated that cancer prevention efforts have the potential to reduce cancer incidence and cancer- related mortality by over 50% and 30% percent, respectively. Although many avoidable exposures are etiologically related to cancer, effective interventions have proven difficult to implement globally. Screening continues to be based primarily on clinical examination followed by histologic assessment of biopsies, perhaps followed by removal of preneoplastic lesions when they exist. However, unlike for advanced disease, effective molecularly driven interventions and risk assessment are not available for clinically normal tissues that may be have been exposed to carcinogens or for preneoplastic lesions. This is because we have not identified the key genomic drivers of progression from normal tissue to preneoplastic lesion to invasive cancer. The long-term goal of this project is use knowledge of key genomic changes that drive early cancer progression to identify and validate novel molecular targets for chemoprevention and risk assessment so that cancer incidences may be decreased. Squamous cell carcinomas (SCC) arising in various organ sites cause over 900,000 deaths worldwide annually. Because stratified squamous epithelia form environmental barriers in the airways, gastrointestinal / genitourinary tracts, and skin, the majority are drivenby carcinogenic exposures such as tobacco and solar radiation. Importantly, previous results and our own data show that SCCs from diverse sites share deep molecular commonalities including alterations in global gene expression and in TP53, TP63, NOTCH, and SOX2 signaling. Cutaneous squamous cell carcinoma (cuSCC) has the most accessible and clinically well-characterized progression sequence of any human cancer, from a distinct precancerous lesion, the actinic keratosis (AK), to invasive carcinoma. Therefore, it is an ideal model for establishing a paradigm of molecularly targeted cancer chemoprevention for SCC. Our central hypothesis is that specific microRNA-mRNA functional pairs and mutational events are key properties of clinically normal, but carcinogen (UV, tobacco) -exposed tissue, and that these are effective chemoprevention targets because they are early drivers of cuSCC development. To test this hypothesis, we have used next generation sequencing to bear on a clinic-pathologically well-defined development sequence that is both accessible and common. Our proposal contains significant innovation in its use of (1) matched isogenic normal skin, AK, and cuSCC from patients to minimize inter-individual variability, (2) a well- characterized UV-driven cuSCC mouse model for comparative and functional analysis, (3) cross-species genomic analysis, and (4) a novel surfactant-based non-invasive skin sampling technology to measure RNA expression and DNA mutations in-vivo. Our team includes expertise in dermatology, dermatopathology, chemical engineering, mouse cancer models, miRNA biology, and bioinformatics.